How moist should a compost pile be?

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How moist should a compost pile be?



You have a compost heap on the go and you make regular additions to it. The mass of the heap will gradually grow and there may be times when you look at it and wonder if it’s moist enough for the compost to form. Excess moisture is unlikely in a free-draining compost bin or tumbler but if the mass is too dry, nothing will happen, the compost won’t form.

So, how moist should a compost pile be? A compost pile should be moist enough for the microbial life forms to function. A simple test is to push a dry wooden stick into the mass and pull it out. Take a close look at the stick and look for signs of moisture. If it’s completely dry, which would be unusual, put the ‘rose’ on the watering can and give the heap a good soak.

There is no need to focus on an exact measurement for compost moisture. Any level of moisture in compost will encourage decomposition, even if it’s just damp. It takes surprisingly little moisture for mould and other fungi to start growing. When you see signs of mould, or fungi, on the surface of green waste on the compost pile, this will be the first stage of the composting process.

In most compost piles, the components that are brought together to make the compost, carry enough moisture without the need to add any extra water. For example, kitchen waste tends to contain more moisture than is needed. You won’t need to add extra moisture to kitchen waste that’s being made into compost.

Any excess moisture in kitchen waste can be absorbed into other dry ingredients, for example shredded paper. This will draw the excess away from the kitchen waste and contain it to make the most of the nutrient value in the surplus liquid. If you don’t do this, the excess moisture will, most likely, drain away and will be lost. The paper will also help the composting process by adding the carbon ’brown’ element, thus achieving the required balance.

If you’re aiming to make compost from just garden trimmings, then, you may have a problem with lack of moisture. This will depend on how much moisture was in the trimmings at the time of being loaded into the compost pile or bin. In most cases, green hedge clippings and lawn clippings will contain sufficient moisture to get the composting process started but in very hot weather the pile may dry out and the process will go into a dormancy.

If this happens, then, you will need to add water to get the process going again. A compost pile of hedge clippings is less likely to dry out if the clippings are put through a shredder. Small particles will compress together, reducing air movement through the mass, where as non-shredded material will stay more open allowing dry air to circulate.

If you have a significant volume of dead, dry leaves and you want to make compost of them without adding any other components that are moist, then, you will have to add water. Be prepared to water them more than once because the first application will mostly drain away. It’s important to ensure that enough water soaks into dry leaves as they tend to be tough, hard and slightly water resistant.

When enough water has been absorbed into a mass of leaves, it will tend to hold onto the moisture because there will be very little air movement, if any, through the pile. There will be enough air for the rotting process to begin and the structure of the pile will change as the leaves gradually convert into compost. Extra applications of water may be necessary. This will depend on the climate conditions, so, you need to inspect the pile and assess whether it looks and feels dry or not.

The same will apply if you’re aiming to make compost from dry grass. This will rot faster if it’s been shredded but it isn’t essential. A pile of dry, long grass will just sit there and do nothing. If you make it wet to the point of run-off, this should be enough to start the composting process. Wet or damp grass will hold onto any moisture as it tends to settle into a compacted mass that will have enough air available to make compost but not enough to allow drying.

How can I test a compost pile for moisture?

There are gadgets that you can buy that will measure the moisture of your, forming, compost but there isn’t really any point using them. You can easily see if the compost pile is moist or dry. Push a stick into the mass. Pull it out and just look at it. If it looks damp, then, the compost is moist enough.

There may be dry material sitting on the top of the pile but this will become moist, especially if you throw in some wet kitchen waste on top of it. If you push a stick into the mass, that should be turning into compost, and it comes out completely dry, then, you need to give it a good drenching of water. This may be more necessary if the pile consists of, mainly, dead, dry leaves. One good drench of water should be enough but it will be worth inspecting by using the stick-probe-test in a couple of days.

Can a compost pile be too moist?

A compost pile can be too moist but this can only happen if there isn’t a good balance of ‘green’ and ‘brown’ material. Too much kitchen waste and not enough shredded paper, or cardboard, will create a mass that is solid and wet. It will become stagnant. The excess of moisture will seal out any air movement.

A high level of moisture in very ‘green’ material will stay in the mass. It won’t, conveniently, drain away and allow the material to dry down to an acceptable level of moisture. This will lead to anaerobic digestion and you will notice a bad smell. This condition is most undesirable and must be avoided if you are serious about making compost. Apart from the smell you will also see masses of flies. If you see this happening, then, you really need to take action.

Adding shredded paper or cardboard will absorb some of the moisture away from the mass. This will open it up and allow some air to get in and encourage microbial activity. When this happens, the material will start to rot and convert into compost.

There is an additional component that you can add that always makes a big difference when making compost, regardless of the state of the pile. That is the addition of hydrated white-lime. This will have the effect of neutralizing the, inevitable, acidity that occurs in a developing compost pile. If your compost is displaying the symptoms of a smell and there are flies, then, you will be amazed at what a liberal sprinkling of white-lime will do.



Should a compost pile be in the shade?

If you are situated in a hot part of the world, then, it would be wise to place your compost pile, or bin, in a shaded area. Constant hot, dry weather will dry out most things, including compost. If a compost pile becomes too dry it will become dormant. There is also the risk that rodent-wildlife may start taking up residence.

Depending on your local-climate conditions, you may find that placing your compost pile in the shade may not be enough to stop dehydration. In such cases, be ready to throw in the occasional bucket of water.

Do I have to use fresh water to moisten a compost pile?

No. Compost can be moistened by water from any source. Here’s an opportunity to use recyclable water from washing-machines and bathwater. The detergents and soap content of such water won’t hinder the progress of microbes turning organic waste into compost.

What else would you like to know?

Can you put broccoli in compost?

Can you put avocado peels in compost?

Can I put eggs in the compost?

Can I put cooked food in the compost?

Can tomatoes be used in compost?

Is it OK to put onions in compost?

Related questions

Does a compost bin need air holes? It’s right to say that compost needs plenty of air for the decomposition process to work. It’s, actually, very difficult to make a compost bin air tight to the point where no air can get in. Establishing a complete vacuum is impossible. There will always be enough air that will find its way in to provide the right conditions over a long period of time. So, given that you haven’t, by chance, achieved vacuum-status with your compost bin, it won’t be necessary to add extra air holes.


Do I need a lid on my compost bin? It’s wise to cover a compost bin, especially if you live in a high rainfall area. Excess moisture from rain over time would be a problem if left uncovered. When you add up the total volume of rain over a year, you will see that it amounts to a considerable level. This will. If allowed to do so, will flush nutrients from the compost. The potential excess water will also hinder the composting process. So, keep a lid on it.

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